1. Field of the Invention
The invention relates to a method for preparing deep-frozen liquid gas, such as for example liquefied natural gas (LNG) or liquefied propane gas (LPG) or even industrial gases, for a downstream technical process.
2. Discussion of Background
In addition to crude oil and its products produced by cracking and coal, nowadays gaseous energy carriers, such as for example natural gas and propane gas, are also used as fuels for power stations or in processes of the steel and chemical industry. Since gases generally have a relatively large volume, they must be sufficiently compressed in order to implement effective transportation and effective storage. Since, however, far more energy is required for the compression of gases than for the compression of liquids, the natural gas and the propane gas are first liquefied. In the process, so-called liquefied natural gas (LNG) or liquefied propane gas (LPG) is obtained. Both transportation and storage of these liquid gases are carried out under atmospheric pressure and at temperatures of about minus 160.degree. C. Accordingly, the respective deep-frozen liquid gas must be vaporized, i.e. regasified, before it is used as fuel.
According to page 9 of the brochure 100-332 2 MCI of the company CHIODA, printed in May 1995 in Japan, under the title "CHIODA in LPG/LNG receiving terminals", a number of evaporation devices are known for each of the deep-frozen liquid gases used, in which devices the energy required to vaporize the low-temperature fuel is supplied in the form of hot water, seawater or additional fuel. After the quantity of heat required for the evaporation operation has been given off, the respective heat-exchange medium is conducted away again, as a result of which its refrigerating capacity is lost from the process.
In contrast, cooling is required in many subprocesses in power stations and in the steel and chemical industry. According to the article "Refrigerated inlet cooling for new and retrofit installations" in the journal Gas Turbine World, Volume 23, No. 3, of May/June 1993, the lowering of the air inlet temperature of a gas turbine plant, i.e. the inlet temperature of the combustion air sucked in by the compressor, leads to a considerable improvement in the power given off and the heat consumption. External coolants, such as stored ice, ammonia, freons, glycol, etc., are used for this purpose. However, the provision, the handling and the environmentally compatible disposal of these additional coolants causes considerable effort and thus costs.